Hydraulic accumulators are readily available commercially in a plurality of embodiments. The essential applications of such hydraulic accumulators are in energy storage, emergency operation, oil leakage compensation, and in energy accumulation and pulsation damping. The most frequently encountered structural forms of hydraulic accumulators are ones with a separating member. A distinction is made between bladder accumulators, diaphragm accumulators, and piston accumulators, as a function of the separating member employed. The mode of operation of all these accumulators is based on utilization of the compressibility of a gas for accumulation of a fluid, nitrogen often serving as energy carrier. Hydropneumatic accumulators include a fluid component and a gas component, and have a gas-tight separating element. The fluid component is connected to the hydraulic network, so that the gas on the gas side in the accumulator is compressed as the pressure increases. Analogously, the compressed gas in the accumulator can expand in the event of a pressure drop on the network side and the accumulated hydraulic fluid is forced back into the network as a result.
The conventional structure of a piston-type accumulator is characterized by an outer cylindrical tube as accumulator housing into which a piston with its compression system is introduced so as to be longitudinally displaceable. Sealing covers on the front sides of the accumulator housing delimit two operating spaces in the accumulator, one of which receives the gas and the other of which is connected to the hydraulic network to conduct fluid.
Damping devices (e.g., diaphragm accumulators SB 0210-0,32E2 manufactured by Hydac) reduce water hammer inside a hydraulic accumulator. At the fluid inlet side of the accumulator, these damping devices have a valve component which may be displaced in the longitudinal direction of the accumulator. The devices are an integral component of the accumulator. The valve component is guided in a valve housing, and is provided with a fluid transfer area. If a water hammer comes from the direction of the hydraulic network, this water hammer reaches the fluid connection area of the hydraulic accumulator. The water hammer in the hydraulic network closes the valve component against the internal fluid pressure of the accumulator. The valve component comes into closing contact with the valve housing. However, as before, but now in throttled form, fluid from the hydraulic network reaches the interior of the accumulator, that is, the fluid side, via a central passage bore as transfer area situated in the valve component.
The water hammer is reduced as a result of the respective throttling of the flow of fluid with the valve component closed by the transfer area in the form of the longitudinal bore. As before, fluid in a smaller amount now continues to flow into the interior of the accumulator. In the opposite situation, that is, when the fluid pressure decreases on the hydraulic network side, the accumulator pressure effects opening of the valve component and fluid flows from the interior of the accumulator housing through cleared larger opening cross-sections in the valve component. An additional portion of the flow of fluid is conducted over the transfer area in the form of a throttle. As a result of configuration of the throttle position in the disclosed solution in the form of a bore of short channel length, turbulences and accordingly cavity phenomena occur on the material components of the valve components and/or accumulator housing adjoining the transfer area. However, in addition to the harmful cavity action, the turbulences also cause disruption of the flow of fluid into and out of the accumulator. This situation may have an adverse effect on the energy balance as a whole of accumulators, as well as of the hydraulic network. In addition, opening and closing of the valve component is associated with a relevant generation of noise, something which may exert a very disruptive effect on operation of such hydraulic assemblies.
DE 102 14 871 A1 discloses a device for damping water hammer, in particular a device in the form of a pressure medium accumulator having a housing. The housing interior is subdivided into two chambers by a medium separation element. The first chamber is filled with a gas. The second chamber is filled with a fluid. In a hydraulic connection, a bottom valve permits filling of the second chamber with fluid and prevents complete emptying of the second chamber. The sealing element of the second chamber may be operated by the medium separation element. In addition, means are provided for throttling the pressure medium volume introduced during the process of filling the second chamber, which means release the full pressure medium volume flow only after the bottom valve has been fully opened.